FIG. 1 schematically shows an internal structure of a conventional non-contact IC card. In FIG. 1, an oscillator circuit 1 generates a clocking oscillation signal 2 which is applied to a CPU 31 in a digital circuit 3. The digital circuit 3 includes, in addition to the CPU 31, a program storage ROM 32, a data storage RAM 33, and an input/output control circuit 34 for transferring to and receiving data from a modulator/demodulator circuit 41 in an analog circuit 4. The CPU 31, the ROM 32, the RAM 33, and the input/output control circuit 34 are coupled to each other by a bus 5. An antenna circuit 42 is provided in the analog circuit 4 for converting an electrical signal from the modulator/demodulator circuit 41 into a radio wave 91 for transmitting data to an external device. The antenna circuit 42 also receives data in the form of a radio wave 92 from the external device. An internal power supply battery 6 continuously supplies operating current to the oscillator circuit 1, the digital circuit 3 and the analog circuit 4 via lines 51, 52, and 53.
Now, the operation of the conventional non-contact IC card of FIG. 1 is described.
Operating current is continuously supplied from the battery 6 to the oscillator circuit 1, the digital circuit 3, and the analog circuit 4. External data to be applied to the non-contact IC card 10 is received in the form of a radio wave 92 by the antenna circuit 42. The antenna circuit 42 converts the received wave into an electrical signal S.sub.E and applies it to the modulator/demodulator circuit 41. The modulator/demodulator circuit 41 demodulates the signal S.sub.E into a digital data signal S.sub.D, which is applied to the input/output control circuit 34. An output data signal from the input/output control circuit 34 is applied via the bus 5 to the CPU 31, which reads the output data signal applied to it for causing a required operation to be executed.
For transmission of data from the non-contact IC card 10 to the external device, a data signal from the CPU 31 is fed via the bus 5 to the input/output control circuit 34, which, in response to the received data signal, applies a digital data signal S.sub.D ' to the modulator/demodulator circuit 41. The modulator/demodulator circuit 41 modulates a carrier with the digital data signal S.sub.D ' to produce a modulated electrical signal S.sub.E ' and sends it to the antenna circuit 42. The antenna circuit 42 converts the modulated signal received from the modulator/demodulator circuit 42 into a radio wave 91 for transmission to the external device. Thus, through the transmission of the wave 91 and the reception of the wave 92, the non-contact IC card 10 can transmit data to and receive data from the external device.
With the above-described arrangement of the conventional non-contact IC card 10, current is continuously supplied from the battery to all of the circuits including the oscillator circuit 1, the digital circuit 3 and the analog circuit 4, even in the standby mode of operation during which the antenna circuit 42 is neither transmitting the wave 91 nor receiving the wave 92, and, therefore, a large amount of power from the battery 6 is consumed, which disadvantageously causes the life of the battery 6 to be short.
Japanese Published Patent Application No. HEI 1-206422 discloses a "portable information device" in which power consumption in a standby mode is reduced. In this portable information device, an operating voltage applied to each circuit is decreased in the standby mode, and the operating voltage to the respective circuits is raised to its nominal value for the normal mode of operation of the device. In this portable information device, however, the application of the operating voltage is not controlled by an external signal, and, even in the standby mode of operation, an operating voltage, although it is low, is supplied to the circuits. Thus, reduction of the power consumption is not sufficient.
Japanese Published Patent Application No. SHO 63-58524 discloses an IC card in which in a standby mode, first clock generating means is operated to generate a lower frequency clock signal, and in response to a key input or to an external signal input, second clock generating means is enabled to generate a nominally higher frequency clock. Thus, the power consumption in the standby operation mode is reduced. In this IC card, too, because a clock signal, though it is at a lower frequency, is generated in the standby mode, the reduction of power consumption as a whole is not sufficient. Furthermore, in this IC card, even in the standby mode, an operating voltage is continuously supplied to an analog circuit in the IC card, which causes a large amount of power to be consumed from an internal battery.
Japanese Published Patent Application No. SHO 62-34292 shows an IC card which comprises an internal switch circuit. The internal switch circuit is turned on in response to an optical signal applied thereto from an external read-out device to cause an operating voltage to be applied from an internal battery to internal circuits, such as a control unit and a memory unit, within the card. Reduction of power consumption in a standby mode may be achieved in this IC card, but, in case the external device operates abnormally, the IC card may respond to the reception of an optical signal from the external device so that the internal battery continues to supply the operating voltage to the respective internal circuits, and, thus, power is wasted.
According to the present invention, a non-contact IC card is provided, in which, not only when the IC card is in the standby mode of operation during which data transfer between the IC card and the external device is not occurring, but also when the external device is in abnormal operation so that data transfer is abnormal or data itself is abnormal, the operation of various units of the IC card is inhibited to thereby reduce power consumption.